1. Field of the Invention
The present invention relates to a method of measuring rotational motion of a golf ball that moves at an ultrahigh speed, in which method the golf ball is photographed in order to analyze the motion of the golf ball.
2. Description of the Related Art
Conventionally, DINAFAX (trade name) is available on the market as an apparatus for photographing a golf ball in a state in which the golf ball moves at an ultrahigh speed, such as an impact state in which the golf ball receives an impact from a swinging golf club. The DINAFAX has a rotatable cylindrical unit, and a film is disposed on the inner circumferential surface of the cylindrical unit. A lens is provided at a position located away from the center of the cylindrical unit along the axial direction thereof. An image obtained through the lens is projected onto the film through a prism. For high speed photography, the cylindrical unit rotates to thereby sequentially photograph images on the film. Also, Japanese Patent Application Laid-Open (kokai) No. 62-104279 discloses a method which uses a high-speed instantaneous multi-image recording apparatus in combination with a video camera and a strobe.
However, the former method involves the process of developing a film and when the motion of an object to be photographed continuously varies at an ultrahigh speed, whether or not the object has been successfully photographed is unknown until development is completed. Accordingly, re-photographing is often required, in turn requiring much labor and time for experimentation. According to the latter method, the strobe flashes repeatedly to photograph a number of images of a dynamic object within one display area (multi-image photography) while the shutter of the video camera is open. Thus, this method can be carried out only in a dark place (in a place having at most the brightness of a room). Also, the apparatus itself is very expensive.
The present invention has been accomplished in view of the above problems, and an object of the present invention is to provide a method of measuring rotational motion of a golf ball capable of being carried out both outdoors and indoors through use of a relatively inexpensive apparatus.
To achieve the object, the present invention provides a method of measuring rotational motion of a golf ball in which a hit golf ball is photographed by use of two cameras disposed along the traveling direction of the golf ball with a predetermined distance therebetween, and the rotational motion of the golf ball is measured based on the photographed images of the golf ball. The method comprises the steps of: providing a golf ball having a no-depression polygonal mark in black or a dark color close to black printed on the surface of the golf ball; hitting the golf ball; photographing the hit golf ball by use of two cameras; detecting the position of an angular point of the no-depression polygonal mark from photographed images, by means of image processing (specifically, automatic image processing performed by use of a computer); and calculating rotational motion of the hit golf ball based on change in position of the angular point in images photographed by the two cameras.
As described above, the method of measuring rotational motion of a golf ball according to the present invention enables automatic measurement which can be carried out both outdoors and indoors through use of a relatively inexpensive apparatus.